To become healthy, in addition to regular exercise, nutritional supplements, and a proper rest, a person should prevent the invasions of external pathogens, such as bacteria or viruses. Killing bacteria and viruses has been applied for a long time to reduce infection. There are many methods to remove microorganisms, including bacteria, viruses and other pathogens. The methods include killing microorganisms directly to reduce their threats to human health, and filtering microorganisms to excluding them from the scope of human life.
Due to the fact that life automatically seeks substainable reproduction, pathogens evolve as the environment updates. Pathogens must rely on water, air or other media to survive and spread. To face the potential threats of pathogens, several methods of killing microorganisms are developed, which are mainly divided into physical methods and chemical methods. The physical methods include filtering and heating. As an example, the heating method can use steam to heat an object to allow the temperature of the object's surface to reach 100 degrees or more. The chemical method can employ bactericides, such as ozone or bleach, to kill microorganisms. However, each method has its limitation and cannot be applied to all cases for killing pathogens. Some methods are difficult to be implemented because of inconvenient operation.
Currently, some manufacturers are dedicated to improve filters used in air conditioning systems, one of which is granted U.S. Pat. No. 9,518,487, wherein a filtering element is provided with a photocatalyst 7 (see FIG. 1), which has good activity. The photocatalyst is irradiated by ultraviolet light so that, when pathogens (such as bacteria or viruses) are carried by an air flow to pass through the filter, the pathogens may react with the photocatalyst. Therefore, the pathogens can be decomposed, and thus the air can be purified. The photocatalyst can be titanium dioxide, activated carbon, or nano silver. The titanium dioxide requires irradiation of ultraviolet light. One example of activated carbon is disclosed in U.S. Pat. No. 8,172,925.
However, the performance of a catalyst depends on whether pathogens are in contact therewith or not. When pathogens contact catalyst, decomposition reaction thereof can be initiated. If the pores of a filter are too large, the pathogens in the air may pass through the pores, without contacting the catalyst on the filter, so that the pathogens can reach a human body and cause a threat to the human body. On the other hand, if the pores of the filter are too small, although the possibility of pathogens contacting the catalyst can be increased, dust or decomposed pathogens are easy to remain on the filter, causing the filter to be blocked. Consequently, the air passing through the filter is quickly reduced. Currently, for increasing the possibility of pathogens contacting a catalyst, a multi-layered filter has been developed. However, this may lead to a large filter, which usually has a higher cost. Particularly, when UVA radiation (wavelength about 315-400 nm) or UVB radiation (wavelength about 280-315 nm) is employed, due to poor penetration of this radiation, the performance of the multi-layered filter can be reduced significantly.
As to UVC radiation (wavelength about 100-280 nm), which has a shorter wavelength and a higher frequency than the previous two types of UV radiation, due to higher energy of each photon, not only does the UVC radiation kill pathogens, also enables the material or electronic components exposed thereunder to age rapidly, thus resulting in photodegradation. In natural world, due to atmospheric protection, the UVC in space cannot reach the surface of the earth. As commonly known, UVC radiation may cause harm to the human body because of its high energy. For UVC radiation, since safety issues associated therewith should be considered more carefully, application of UVC radiation is limited. Another problem in using ultraviolet light is light attenuation, which is resulted from dissipation during transmission. The lost energy during transmission of ultraviolet light cannot be used on sterilization.
Accordingly, it is expected that today's sterilization method can effectively and completely eliminate the threats caused by pathogens, and the method will not cause damages to other objects. In addition to an effective process, the sterilization method should guarantee the safety of human beings and other associated members, and this is one goal that the present invention seeks to achieve.